In recent years, a digital camera equipped with a CCD has been widely used not only for research purposes but also for general purposes. The inside of the camera for research purposes is often cooled down to minus 70 degrees Celsius in order to get the best performance of the CCD.
FIG. 1 is a perspective view of a known CCD camera, and reference numbers 101, 102, 103, and 104 represent a vessel, a front flat glass sheet, an evacuated portion, and a CCD sealed in a vacuum, respectively.
With this structure, the vessel 101 having the CCD 104 stored therein is evacuated close to a vacuum. The flat glass sheet 102 is provided in front of the CCD 104 so as to tightly seal the vessel 101. Since the inside of the CCD camera is cooled, when the humidity of outside air 105 exceeds a certain limit, dew or droplet of water is formed on the glass sheet 102 even when the humidity of the outside air 105 is not 100%, thereby making the CCD camera useless. To avoid the above-mentioned phenomenon, a variety of methods have been devised and applied. For example, a method of blowing dry nitrogen gas onto a glass surface, a method of blowing heated air onto a glass surface, a method of heating the entire CCD camera, and so forth were devised.